In recent years, thermoplastic elastomers have been used as elastomers having rubber elasticity, requiring no curing, and having excellent moldability and workability like thermoplastic resins, in the fields of automotive parts, household electrical appliance parts, electric wire coverings, medical device parts, miscellaneous goods, footwear and so forth. As such thermoplastic elastomers, Japanese Kokai Tokkyo Koho S61-34050, for instance, describes thermoplastic elastomers containing a vinyl aromatic compound block (hard segment) and a conjugated diene compound block (soft segment) alternately in the copolymer chain. In the case of these thermoplastic elastomers, products meeting various specifications, ranging from those rich in flexibility to rigid ones, can be produced by varying the proportions of the two segments appropriately. However, those thermoplastic elastomer compositions containing the soft segment in large proportions are low in tensile strength, heat resistance, flowability and oil resistance and therefore cannot be used in a broad range of applications.
Further, compositions resulting from melt-kneading a monoolefin copolymer rubber and a polyolefin resin together with an organic peroxide as a rubber auxiliary crosslinking agent to thereby effect partial crosslinking are described in Japanese Patent Publication S53-21021, for instance.
Such thermoplastic elastomers in which the monoolefin copolymer rubber has been only partially crosslinked are not satisfactory enough in oil resistance, form recovery at high temperature, and other properties, and hence cannot be used in a sufficiently wide range of applications. The radicals formed from the organic peroxide used for crosslinking cause polymer chain cleavage, hence a reduction in mechanical strength.
Furthermore, it is described in Japanese Patent Publication S58-415138 that the monoolefin copolymer rubber alone is preferentially crosslinked using a heat-reactive alkilphenol resin as the crosslinking agent to thereby overcome the drawbacks mentioned above. Thus, there are described thermoplastic elastomers obtained by crosslinking the EPDM rubber component of a thermoplastic resin preferentially using a phenolic curing agent. The thermoplastic elastomers obtained by such a procedure in which the rubber component has been completely crosslinked show improved oil resistance and form recovery at high temperature but the improvements attainable are not satisfactory enough when compared with cured rubbers.
In U.S. Pat. No. 4,803,244, there are described thermoplastic elastomers obtained by crosslinking the rubber component comprising a monoolefin copolymer using an organosiloxane. However, the matrix components of the thermoplastic elastomers described there are polypropylene, polyethylene, ethylene-.alpha.-olefin copolymers and the like, hence the elastomer compositions show a low rate of recovery after compression. Even when a monoolefin copolymer having relatively good compatibility with the matrix components is used as the rubber component in said elastomer compositions, the dispersion of the rubber component is insufficient because of the poor compatibility of the crystalline fraction of the matrix. In particular, the state of dispersion worsens as the proportion of rubber increases, failing to give physical properties necessary for automotive parts, such as weather strips and dust boots, for which rubber elasticity is particularly needed.
U.S. Pat. Nos. 4,970,263 and 4,500,688 also describe thermoplastic resin compositions in which the rubber component has been crosslinked using an organosiloxane compound as the crosslinking agent. However, in the compositions described therein, a polyolefin or the like is used as the matrix, and the rate of recovery after compression at high temperature is low.
Further, Japanese Kokai Tokkyo Koho H01-236250 describes elastomer compositions in which a thermoplastic resin prepared by grafting a hydrolyzable silane to polyethylene or the like is used as the matrix, with rubber particles crosslinked with a curing agent incapable of curing the silane-grafted polymer, for example sulfur, being dispersed in said matrix. This literature describes only the curing using sulfur, isocyanates or the like and the technology fails to attain high-temperature, high-speed curing, and may possibly meet with the problem of sulfur bleeding. The range of application of the end products is thus limited.
Japanese Kokai Tokkyo Koho H01-217053 also describes elastomer compositions comprising a matrix composed of a hydrolyzable silane group-containing polyolefin resin and another polyolefin resin and a dispersed phase composed of a rubber. However, the rubber phase is phenol-crosslinked. There is no description of SiH crosslinking.